Method for recovering a gaseous pressure product by low-temperature separation of air

ABSTRACT

The invention relates to production of a pressurized gaseous oxygen product by low-temperature separation of air in a distillation column system, having a low-pressure column and a high-pressure column. A first partial stream of the purified feed air is work-expanded in a first expander, and at least partially introduced into the high-pressure column. A second partial stream is cooled in a main heat exchanger to an intermediate temperature, further compressed, cooled in the main heat exchanger where it is liquefied or pseudo-liquefied, and then introduced into the distillation column system. A third partial stream of the compressed feed air is work-expanded in a second expander. A liquid oxygen product stream, removed from the distillation column system, is brought to an elevated pressure, evaporated or pseudo-evaporated in the main heat exchanger, heated to approximately ambient temperature, and ultimately withdrawn as a pressurized gaseous oxygen product stream.

SUMMARY OF THE INVENTION

The invention relates to a method for recovering a pressurized gaseous product by low-temperature separation of air in a distillation column system having has at least one low-pressure column and a high-pressure column.

Specifically, the invention relates to method wherein an air feed stream is compressed in an air compressor, the resultant compressed feed air is purified at least in part in a purification system, and at least a part of the purified air is further compressed in a warm booster compressor. A first partial stream of the purified air is depressurized in a work-expansion manner in a first expander and is at least partially introduced into the high-pressure column. A second partial stream of the purified air is cooled in a main heat exchanger to an intermediate temperature, further compressed in a cold compressor, further cooled in the main heat exchanger where it is liquefied or pseudo-liquefied, and then is introduced into the distillation column system. A third partial stream of the compressed feed air is depressurized in a work-expansion manner in a second expander. A liquid oxygen product stream is removed from the distillation column system, brought to an elevated pressure in a liquid state, evaporated or pseudo-evaporated under this elevated pressure in the main heat exchanger, heated to approximately ambient temperature, and ultimately drawn off as a pressurized gaseous oxygen product stream. The two expanders are each coupled to one of the two machines, the warm booster compressor and the cold compressor.

Methods and devices for low-temperature separation of air are known from, for example, Hausen/Linde, Tieftemperaturtechnik [Low-Temperature Technology], 2^(nd) Edition 1985, Chapter 4 (pages 281 to 337).

The distillation column system of the invention can be designed as a two-column system (for example as a standard Linde double-column system) or else as a three-column or multiple-column system. In addition to the columns for nitrogen-oxygen separation, additional devices can be provided to recover extremely pure products and/or other air components, in particular noble gases, for example an argon and/or a krypton-xenon recovery.

In the process, an oxygen product stream that is in the liquid state is evaporated using a heat transfer medium and ultimately recovered as a pressurized gaseous product. This method is also referred to as internal compression. It is used for recovering high-pressure oxygen. For the case of a supercritical pressure, no phase transition takes place in the actual sense; the product stream is then “pseudo-evaporated.”

Opposite the (pseudo)-evaporating product stream, a heat transfer medium that is under high pressure is liquefied (or pseudo-liquefied, when it is below supercritical pressure). The heat transfer medium is frequently formed by a part of the air feed stream, in this case by the “second partial stream” of the compressed feed air.

Internal compression methods are known from, for example, DE 830805, DE 901542 (=U.S. Pat. No. 2,712,738/U.S. Pat. No. 2,784,572), DE 952908, DE 1103363 (=U.S. Pat. No. 3,083,544), DE 1112997 (=U.S. Pat. No. 3,214,925), DE 1124529, DE 1117616 (=U.S. Pat. No. 3,280,574), DE 1226616 (=U.S. Pat. No. 3,216,206), DE 1229561 (=U.S. Pat. No. 3,222,878), DE 1199293, DE 1187248 (=U.S. Pat. No. 3,371,496), DE 1235347, DE 1258882 (=U.S. Pat. No. 3,426,543), DE 1263037 (=U.S. Pat. No. 3,401,531), DE 1501722 (=U.S. Pat. No. 3,416,323), DE 1501723 (=U.S. Pat. No. 3,500,651), DE 253132 (=U.S. Pat. No. 4,279,631), DE 2646690, EP 93448 B1 (=U.S. Pat. No. 4,555,256), EP 384483 B1 (=U.S. Pat. No. 5,036,672), EP 505812 B1 (=U.S. Pat. No. 5,263,328), EP 716280 B1 (=U.S. Pat. No. 5,644,934), EP 842385 B1 (=U.S. Pat. No. 5,953,937), EP 758733 B1 (=U.S. Pat. No. 5,845,517), EP 895045 B1 (=U.S. Pat. No. 6,038,885), DE 19803437 A1, EP 949471 B1 (=U.S. Pat. No. 6,185,960 B1), EP 955509 A1 (=U.S. Pat. No. 6,196,022 B1), EP 1031804 A1 (=U.S. Pat. No. 6,314,755), DE 19909744 A1, EP 1067345 A1 (=U.S. Pat. No. 6,336,345), EP 1074805 A1 (=U.S. Pat. No. 6,332,337), DE 19954593 A1, EP 1134525 A1 (=U.S. Pat. No. 6,477,860), DE 10013073 A1, EP 1139046 A1, EP 1146301 A1, EP 1150082 A1, EP 1213552 A1, DE 10115258 A1, EP 1284404 A1 (=US 2003051504 A1), EP 1308680 A1 (=U.S. Pat. No. 6,612,129 B2), DE 10213212 A1, DE 10213211 A1, EP 1357342 A1 or DE 10238282 A1, DE 10302389 A1, DE 10334559 A1, DE 10334560 A1, DE 10332863 A1, EP 1544559 A1, EP 1585926 A1, DE 102005029274 A1, EP 1666824 A1, EP 1672301 A1, DE 102005028012 A1, WO 2007033838 A1, WO 2007104449 A1, EP 1845324 A1, DE 102006032731 A1, EP 1892490 A1, DE 102007014643 A1, A1, EP 2015012 A2, EP 2015013 A2, EP 2026024 A1, WO 2009095188 A2, or DE 102008016355 A1.

The term “expander” comprises any machine for the work expansion stage of a process stream. The expanders used in the invention are preferably formed by expansion turbines.

The “main heat exchanger” can be formed from one or more parallel- and/or serially-connected heat-exchanger sections, for example from one or more plate heat-exchanger blocks. It serves to cool the feed air streams in indirect heat exchange with backflows from the distillation column system.

This application also hereby incorporates the disclosure of the German patent application DE 10 2020 52545.6, filed Nov. 25, 2010, which is referred to as “parallel application” below, as well as the disclosure of the applications that correspond to this parallel application.

A method of the above-mentioned type is known from WO 2008110734 A2. In this process, it is decisive that the second expander can be turned off, and the entire third partial stream is blown off downstream from the second expander into the atmosphere so that it does not disrupt rectification.

The object underlying the present invention is therefore to provide a method of the above-mentioned type, as well as a corresponding apparatus, which are to be operated especially advantageously economically.

Upon further study of the specification and appended claims, other objects and advantages of the invention will become apparent.

These objects are achieved by a method for producing a gaseous oxygen pressure product by low-temperature separation of air in a distillation column system, having at least one low-pressure column and a high-pressure column (80), wherein in the method:

process feed air (1) is compressed in an air compressor (2),

the compressed feed air (3) is purified at least in part in a purification system (5),

at least a part (7) of the purified feed air (6) is further compressed in a warm booster compressor (8),

a first partial stream (11, 15) of the purified feed air (6) is depressurized in a work-expansion manner in a first expander (16) and is at least partially introduced (17) into the high-pressure column (80),

a second partial stream (12) of the purified feed air (6) is cooled in a main heat exchanger (14) to an intermediate temperature, further compressed in a cold compressor (19), further cooled in the main heat exchanger (14), and liquefied or pseudo-liquefied and then is introduced into the distillation column system (21, 23),

a third partial stream (13) of the compressed feed air (3) is depressurized in a work-expansion manner in a second expander (25),

a liquid oxygen product stream (30, 32) is removed from the distillation column system, brought to an elevated pressure in a liquid state (34), evaporated or pseudo-evaporated under this elevated pressure in the main heat exchanger (14), heated to approximately ambient temperature, and ultimately drawn off as a gaseous pressurized oxygen product stream (33),

the two expanders (16, 25) are each coupled to one of the two machines, the warm booster compressor (8) and the cold compressor (18, 19), and

at least one part of the work-expansion depressurized third partial stream (26) is returned to the air compressor (28).

In the method according to the invention, at least one part of the air from the second expander (third partial stream) is not discarded but rather is recycled into the air compressor. Thus, on the one hand, the yield of the unit is increased; on the other hand, the second expander can be operated as before with an especially low exit pressure, thus with a relatively high output.

Preferably, the exit pressure of the second expander is approximately equal to the operating pressure of the low-pressure column (plus line losses). Generally, the exit pressure of the second expanded is between the operating pressure of the low-pressure column and 0.5 bars above such operating pressure, for example, 1.2 to 1.8 bars.

Within the framework of the invention, the entire third partial stream can be introduced into the air compressor. Preferably, at least 30 mol %, in particular at least 50 mol %, of the work-expanded third partial stream is introduced into the low-pressure column. (At this point, the entire air stream that is run through the second expander is referred to as a “third partial stream.”)

The portion of the work-expanded third partial stream that is not feed back to the air compressor, or a part thereof, can be fed into the low-pressure column.

The feeding of the work-expanded third partial stream (or a part thereof) into the air compressor can be done, for example, at the intake. As an alternative, this feeding takes place at an intermediate stage of the air compressor, whereby the air compressor is designed in multiple stages and has at least a first and a last stage, whereby at least one part of the work-expanded third partial stream is recycled to the air compressor downstream from the first stage and upstream from the last stage.

The branching-off of the third partial stream from the feed air can be performed, for example, downstream from the purification device. For example, branching-off of the third partial stream can be carried out directly upstream of the booster compressor, downstream from the booster compressor and upstream of the first expander, or else downstream from the first expander. In particular, the third partial stream is branched-off, however, from the compressed feed air at a point upstream of the purification system.

Air separation units of the above-mentioned type commonly have a pre-cooling device in which the compressed feed air is cooled upstream from the purification device by direct or indirect heat exchange with cooling water to remove the compression heat. In this case, the third partial stream can be branched-off from the purified feed air upstream from the pre-cooling device. This feature of the invention, namely the branching-off of a partial air stream upstream from the pre-cooling system with a subsequent work-expansion stage and recycling to the air compressor and/or discharging into the atmosphere can basically be applied in any low-temperature air separation method, even without the features further cited above; this applies in particular when cold is produced in another expander (here: the first expander), and two expanders are coupled mechanically to the booster compressors, in particular one with a cold compressor and the other with a warm booster compressor.

As an alternative or in addition, a part of the work-expansion third partial stream is discharged into the atmosphere. This can be useful in particular when the exit pressure of the second expander is at the level of the low-pressure column pressure.

In the method according to the invention, the entire feed air can be further compressed in a body in the warm booster compressor, i.e., in particular the first, the second and the third partial streams. (Parts of the air that are optionally branched-off for other purposes, so-called instrument air, are not counted here in the “entire feed air.”) The branching-off of the third partial stream from other parts of the feed air then takes place downstream from the warm booster compressor. This procedure is in particular useful in serial connection of the turbines, but it can also be used when the turbines are connected in parallel.

As an alternative, the first and the second partial streams are further compressed in the warm booster compressor, and the third partial stream by-passes the warm booster compressor. The branching-off of the third partial stream from the other air parts in this case occurs upstream from the warm booster compressor.

In another embodiment of the invention, the second partial stream is further compressed in the warm booster compressor, and the first and third partial streams by-pass the warm booster compressor. The branching-off of the third partial stream from the other air parts can also take place upstream from the warm booster compressor, or can occur downstream from the common branching-off of the first and third partial streams from the purified, but not further compressed feed air stream.

For example, the third partial stream is introduced into the second expander at, for example, the exit pressure of the air compressor or at, for example, the exit pressure of the warm booster compressor. In this case, the splitting into the first and third partial streams occurs upstream from the work-expansion stages. The two expanders are connected in parallel.

As an alternative, the third partial stream together with the first partial stream is expanded in the first expander, the first and third partial streams are then split, and the third partial is expanded in the second expander, separately from the first partial stream. The splitting into the first and third partial streams may also be performed upstream from the first expander. The two expanders can be connected in series.

Preferably, in the method, the feed air compressor represents the only machine driven by external energy for compressing the air. “Only machine” is defined here as a one-stage or multi-stage compressor whose stages are all connected to the same drive, whereby all stages are installed in the same housing or connected to the same gear. In this feed air compressor, preferably the overall feed air is compressed to a pressure that is clearly above the highest pressure of the distillation column system, in particular clearly above the operating pressure of the high-pressure column. This pressure difference between the exit pressure of the feed air compressor and the operating pressure of the high-pressure column is, for example, at least 4 bar and is preferably between 6 and 16 bar. In this variant, the total air that is compressed in the feed air compressor (up to possible smaller portions such as, for example, instrument air) is preferably completely divided into three partial streams.

In addition, in the method, an internal nitrogen compression can be supplemented by a liquid nitrogen product stream removed from the distillation column system, brought in a liquid state to an elevated pressure, evaporated or pseudo-evaporated at this elevated pressure in the main heat exchanger, heated to approximately ambient temperature, and finally drawn off as a gaseous nitrogen-pressure product stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated schematically with reference to an exemplary embodiment in the drawing and will be described extensively hereinafter with reference to the drawing. Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawing wherein:

FIG. 1 shows a first embodiment of the invention with branching-off of the third partial stream upstream from the pre-cooling, and

FIGS. 2 to 4 show three additional embodiments with branching-off of the third partial stream upstream from the pre-cooling.

In FIG. 1, atmospheric air is delivered as process feed air via line 1 to an air compressor 2 and compressed therein to a pressure that is significantly higher than the operating pressure (e.g., 6 bar) of the high-pressure column 80 (“HPC”). The air compressor is designed in multiple stages here, in particular four, five or six stages, whereby one intermediate condenser each is located between the stages. A larger portion 42 of the compressed feed air 3 is fed to a pre-cooling device 4 (“Precooling”), in which the compression heat of the last stage of the air compressor is removed by a direct or indirect heat exchange with cooling water. The pre-cooled feed air is purified in a purification system 5, which preferably is designed as a molecular sieve adsorber (“MS-Adsorber”). The compressed feed air 3 is divided into three partial streams in the embodiment:

-   -   After cooling in a main heat exchanger 14, a first partial         stream 11 is fed at a first intermediate temperature via line 15         to the work-expansion stage, first expander 16, and then         introduced via line 17 into the high-pressure column 80 (“HPC”)         of the distillation column system.     -   In the main heat exchanger 14, a second partial stream 12 is         cooled to a second intermediate temperature, that is lower or         higher or equal to the first intermediate temperature, removed         from the main heat exchanger 14 via line 18, further compressed         in a cold compressor 19, introduced again via line 20 into the         main heat exchanger 14 at a third intermediate temperature,         which is higher than the second intermediate temperature, and         further cooled therein and finally liquefied or—if the pressure         of the second partial stream is supercritical—pseudo-liquefied.         The (pseudo-) liquefied second partial stream 21 is         depressurized in a butterfly valve 22 to approximately the         pressure of the high-pressure column 80 (“HPC”). and finally         introduced into the high-pressure column 80 (“HPC”). A part of         the depressurized third partial stream 23 can also be injected         directly into the low-pressure column 90 (“LPC”) of the         distillation column system.     -   A third partial stream 13 of the compressed feed air 3 is         branching-off directly upstream of the pre-cooling device 4         (“Precooling”), and fed, without cooling in the main heat         exchanger 14, into a second expander 25 of the work-expansion         stage. The third partial stream 26 that is depressurized in a         work-expansion manner to a pressure of, for example, 1.2 to 6         bar, preferably approximately 1.3 bar, is completely fed, in the         example of FIG. 1, via line 28 to the air compressor 2 and         introduced there into the total air stream, for example, at a         point upstream of the last stage, in particular downstream from         an intermediate condenser, which is operated under appropriate         pressure.

The first and second partial streams 11, 12 are run here together via the lines 7 and 10 from the exit of the purification system 5 through a warm booster compressor 8 with a secondary condenser 9 to the hot end of the main heat exchanger 14.

A liquid oxygen product stream 30 is removed from the low-pressure column 90 (“LPC”), brought in a liquid state to an elevated pressure in a pump 31 (52), evaporated under this elevated pressure in the main heat exchanger 14 or, if the pressure is higher than the critical pressure, pseudo-evaporated, heated to approximately ambient temperature, and finally drawn off as a gaseous pressurized oxygen product stream 33.

Also, a nitrogen pressure product can be obtained by means of internal compression. To this end, a liquid nitrogen product stream is removed from the high-pressure column 80 (“HPC”) or its top condenser, brought in a liquid state to an elevated pressure in a pump, evaporated under this elevated pressure (line 41) in the main heat exchanger 14 or, if the pressure is higher than the critical pressure, pseudo-evaporated, heated to approximately ambient temperature, and finally removed as gaseous pressurized nitrogen product stream (42).

Further return streams from the distillation column system shown in FIG. 1 are gaseous oxygen 34, impure nitrogen 35, and pure nitrogen 36. These gaseous products are heated in the main heat exchanger 14 to approximately ambient temperature and finally drawn off via the lines 37, 38 and 39. In addition, liquid oxygen and liquid nitrogen can be removed both from the high-pressure column 80 (“HPC”) and from the low-pressure column 90 (“LPC”).

In the facultative passage group 40 of the main heat exchanger 14, the first and second partial streams 7 can be pre-cooled upstream from the warm booster compressor 8. The secondary condenser then can become unnecessary under certain circumstances.

FIG. 2 differs from FIG. 1 in the following detail:

-   -   The first partial stream 11 by-passes the warm booster         compressor 8 via line 210.     -   The third partial stream 13 is branched-off from the second         partial stream 7, 12 at a point downstream from the pre-cooling         4 and purification system 5, and then run via line 210 together         with the first partial stream to the hot end of the main heat         exchanger 14. Then, the third partial stream 13 is cooled in the         main heat exchanger 14 to an intermediate temperature and         delivered via line 24 at this intermediate temperature to the         work-expansion stage 25.     -   The work-expansion third partial stream 28 is heated in the main         heat exchanger 14 to approximately ambient temperature and flows         back via line 29 to the air compressor 2.     -   One less return stream from the distillation column system is         run through the main heat exchanger 14 (Compare lines 41/42 in         FIG. 1).

FIG. 3 differs from FIG. 2 in the following detail:

-   -   The third partial stream 13 is not cooled in the main heat         exchanger 14 before being subjected to the work-expansion stage         25, but rather third partial stream 13 is delivered directly to         the expander.     -   Only a first part of the work-expanded third partial stream 26         is handled via the lines 28 and 29 as in FIG. 2; a second part         of the work-expanded third partial stream 26 is directed via the         lines 27, 227 through the cold part of the main heat exchanger         14 to the low-pressure column 90 (LPC) of the distillation         column system.

FIG. 4 differs from FIG. 2 in the following detail:

-   -   The work-expanded third partial stream 28 is recycled via line         329 to the inlet of the air compressor 2.

All embodiments of the above-mentioned parallel application that show the recycling of at least one part of the work-expanded third partial stream to the air compressor are also embodiments of this invention, are thus are hereby inorportaed by reference. Always when the third partial stream is not further compressed upstream from the second expander, it can be branched-off from the compressed feed air analogously to the accompanying drawing here upstream from the purification device and either upstream or downstream from the pre-cooling device.

As a variant to all embodiments, one or more parts of the work-expanded third partial stream 26 can, at other points in the air compressor, be directed into the low-pressure column 90 and/or into the atmosphere.

The entire disclosure[s] of all applications, patents and publications, cited herein and of corresponding German Application No. DE 10 201 0 052544.8, filed Nov. 25, 2010 are incorporated by reference herein.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 

1. A method for producing a gaseous oxygen pressure product by low-temperature separation of air in a distillation column system having at least one low-pressure column (90) and a high-pressure column (80), said method comprising: Compressing process feed air (1) in an air compressor (2), Purifying the compressed feed air (3), at least in part, in a purification system (5), Further compressing at least a part (7) of the purified feed air (6) in a warm booster compressor (8), Depressurizing a first partial stream (11, 15) of the purified feed air (6) in a work-expansion manner in a first expander (16) and then at least partially introducing (17) the depressurized first partial stream into the high-pressure column (80) of the distillation column system, Cooling a second partial stream (12) of the purified feed air (6) in a main heat exchanger (14) to an intermediate temperature, further compressing the cooled second partial stream in a cold compressor (19), further cooling the second partial stream in the main heat exchanger (14), whereby it is liquefied or pseudo-liquefied, and then introducing the liquefied or pseudo-liquefied second partial stream into the distillation column system (21, 23), Depressurizing a third partial stream (13) of the compressed feed air (3) in a work-expansion manner in a second expander (25), Removing a liquid oxygen product stream (30, 32) from the distillation column system, bringing the liquid oxygen product stream to an elevated pressure in a liquid state (34), evaporating or pseudo-evaporating the liquid oxygen product stream under this elevated pressure in the main heat exchanger (14), heating the evaporated or pseudo-evaporated oxygen product stream to approximately ambient temperature, and ultimately removing the evaporated or pseudo-evaporated oxygen product stream as a gaseous oxygen-pressure product stream (33), Wherein the two expanders (16, 25) are each coupled to one of the two machines, the warm booster compressor (8) and the cold compressor (18, 19), and Wherein at least one part of the work-expanded third partial stream (26) is returned to the air compressor (2).
 2. The method according to claim 1, wherein the air compressor (2) has a plurality of stages comprising at least a first and a last stage, whereby at least one part of the work-expanded third partial stream (26) is recycled to the air compressor (2) downstream from said first stage and upstream from said last stage (28).
 3. The method according to claim 1, wherein the third partial stream (13), upstream from the purification system (5), is branched-off from the compressed feed air (3).
 4. The method according to claim 2, wherein the third partial stream (13), upstream from the purification system (5), is branched-off from the compressed feed air (3).
 5. The method according to claim 3, wherein a part (6) of the compressed feed air (3), which comprises the first and second partial streams, is cooled upstream from the purification system (5) in a pre-cooling device (4), and the third partial stream (13) upstream from the pre-cooling device (4) is branched-off from the compressed feed air (3).
 6. The method according to claim 4, wherein a part (6) of the compressed feed air (3), which comprises the first and second partial streams, is cooled upstream from the purification system (5) in a pre-cooling device (4), and the third partial stream (13) upstream from the pre-cooling device (4) is branched-off from the compressed feed air (3).
 7. The method according to claim 1, wherein a part of the work-expanded third partial stream (26) is discharged into the atmosphere.
 8. The method according to claim 1, wherein the first and second partial streams are further compressed in the warm booster compressor (8), and the third partial stream (13) by-passes the warm booster compressor (8).
 9. The method according to claim 1, wherein the second partial stream is further compressed in the warm booster compressor (8), and the first partial stream by-passes the warm booster compressor.
 10. The method according to claim 1, wherein the third partial stream (13) is introduced into the second expander (25) at approximately the exit pressure of the air compressor (2).
 11. The method according to claim 1, wherein the air compressor (2) represents the only machine driven by external energy for compression of air.
 12. The method according to claim 1, wherein a liquid nitrogen product stream is removed from the distillation column system, brought to an elevated pressure in the liquid state, evaporated or pseudo-evaporated under this elevated pressure in the main heat exchanger, heated to approximately ambient temperature, and finally withdrawn as a gaseous pressurized nitrogen product stream. 